This invention relates generally to the noise control in a copier or image output terminal (IOT), and more particularly concerns an improved noise control system utilizing an improved method and apparatus for providing optimum noise control in such apparatuses by masking the pure tones of charging devices.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
The foregoing generally describes a typical black and white electrophotographic printing machine. With the advent of multicolor electrophotography, it is desirable to use an architecture which comprises a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image on image system in which the photoreceptive member is recharged, reimaged and developed for each color separation. This charging, imaging, developing and recharging reimaging and developing is usually done in a single revolution of the photoreceptor as compared with multipass architectures which allow image on image to be achieved with a single charge, recharge system and imager, etc. This architecture offers a high potential for throughput and image quality.
Charging and recharging IOT systems require a number of charging stations with attendant noise produced by those charging stations. Excessive noise from machines, such as, copier/printers in the working environment has been an irritant to others from the advent of such machines until the present day. One of the major contributors had been found to be the charging systems in the machines. Historically, noise from systems comes from the transformer and chock which can be controlled by an enclosure. However, in some systems noise is emitted from the wires of corona devices. Historically, noise from charging devices has been a problem, especially pure tone noise. In some copier/printers, modulation in charge frequency and amplitude creates beat, which makes the problem even more pronounced and complicated. Pure tone as used herein is noise at one or more discrete frequencies. A prior solution to this problem includes injecting white noise as background to mask the pure tone, but this will not only increase cost but also drive up the overall noise level of the machine which is undesirable. At 4 kHz, this is beyond the capability of active noise control. Another attempted solution is to control noise by absorption. However, pure tone is still audible. It is believed that all charging devices in some machines will be charged at about 4 kHz with the pure tone and beat from the charging devices causing operator discomfort. The pure tone at the operator position is about 60 dB. As machines speed up, the pure tone problem will become even more annoying.
The following disclosures may be relevant to various aspects of the present invention: